It's not currently possible to edit the name of a bookmark, once created. Workaround is to create a new one and add the contents of the old one to it (has to be done one at a time).
Found this out when I decided to use a letter-naming system* to organize recipe bookmarks -- blessedly before I had too many entries in any one bookmark.
c. - cookbook (favorites or want-to-try from a particular book)
m. - menu
i. - ingredient-based
r. - recipe (e.g., slaw, cornbread, etc.)